The primary means by which most neurons communicate with their target cells is through the regulated release of neurotransmitter from synapses. Modulation of the release properties of these synapses has long been postulated, and in certain circumstances been directly demonstrated, to be a critical component of the cellular mechanisms that underlie learning and memory. A molecular understanding of the mechanisms which mediate this release process is crucial to developing a comprehensive understanding of brain function both in health and disease. A decade of molecular studies of the presynaptic terminal has led to the identification of over twenty gene products that are implicated in the release process at the nerve terminal. The role of most of these proteins in regulating release still is unknown. The objective of this grant proposal is to investigate the role of proteins in the release process. Homologs of most of the molecules implicated in this process are present in the nematode. Caenorhabditis elegans. This proposal aims to utilize molecular genetic tools available for the study of C. elegans to examine the role of these proteins in synaptic function. Nematode mutants lacking a number of synapse-associated components including syntaxin, synaptobrevin, rab-3 and rabphilin have been isolated and characterized. Analysis of these mutants that some of these molecules play crucial roles in neuronal function, while others appear to be dispensable. Building upon this foundation of mutants previously isolated in C. elegans, we propose to isolate additional mutants lacking synapse-associated components and to characterize the neuronal defects of animals lacking these molecules. Secondly, we propose to identify molecules that act as negative regulators of the synaptic release process, through the genetic and molecular characterization of suppressors of mutants in the gene encoding syntaxin, a protein central to the function of the nerve terminal. Finally, we propose several lines of experimentation aimed at dissecting the molecular mechanisms which govern how neurons localize these synaptic proteins specifically at the nerve terminal. Our molecular genetic approach of examining synaptic function is complementary to the biochemical approaches that many researchers use to study this highly conserved process.